The biochemical and ultrastructural demonstration of collagen during early heart development

A correlative ultrastructural and biochemical study was made of cardiac collagen in the chick embryo, spanning stages 9- to 11 (6 to 13 somites). Analysis (carboxymethyl cellulose chromatography, SDS acrylamide gel electrophoresis and levels of proline hydroxylation) of collagen synthesized in situ permitted classification of this collagen as type I-like (α1:α2 = 2:1). Correlative electron microscopy of hearts fixed in situ showed the appearance of striated collagen fibrils in the cardiac jelly, thus complementing the biochemical findings. Although the electron microscope showed the presence of developing basal laminae and laminalike material, synthesis of the type of collagen reported as unique to basal laminae was not detected, and we propose that these basal laminae may lack type IV collagen. Embryonic stages 9- to 11 are the earliest stages in which collagen synthesis has been demonstrated, and this is the first report of the occurrence of collagen in cardiac jelly of early hearts.